The present invention relates to a fine processing apparatus for optically and chemically performing addition processing and removal processing of metal or the like in a solution in order to produce a patterned structure having a high aspect ratio, which is especially used in fields in which structures are fabricated using micromachining techniques.
One example of a conventional fine processing apparatus is shown in FIG. 3.
A sample, or workpiece, 10, a counter electrode 32 and a reference electrode 31 are immersed in a solution (plating solution) 16, the electric potential of the counter electrode 32 is set in a state of an equilibrium electric potential or a small overvoltage of a value at which no deposition occurs, and light 1 from a laser apparatus 20 is concentrated and irradiated onto sample 10 through a lens 21. The plating speed rapidly increases at the portion irradiated by the light 1, and a substance is deposited, or plated, only at the irradiated portion. At this time, when the laser beam is made to scan the surface of sample 10, a linear pattern of deposited substance can be drawn.
The principle of this deposition can be explained as follows. Namely, when the laser irradiates the electrode surface of the sample in the solution, and its energy is absorbed by the irradiated portion of the sample, the interface between the electrode and the solution is locally heated. The local heating promotes the electric charge migration reaction which results in the deposition.
However, in the conventional fine processing method, as shown in FIG. 4, the deposited substance 5 having a film thickness distribution as shown in the FIG. 4 is generated at the surface portion of sample 10 which is irradiated by the light. This is considered to be due to the temperature distribution in accordance with the light irradiation. In the case of a raw material having good heat conductivity, the heat generated by the absorption of the light is rapidly diffused. Thus, the film is formed to have a shape extending over the irradiated portion. In addition, in the case of laser light, the intensity of the laser beam gives a normal Gaussian distribution, so that the film thickness distribution provides a hill-like cross section as shown in FIG. 4.
Thus, in order to suppress the influence of the heat diffusion, there have been tried a method in which a substance having low heat conductivity is thinly coated on the sample, a method in which a pulse oscillation laser is used to make the heat release satisfactory so as to decrease the influence of the heat diffusion etc.; however, no satisfactory solution has been achieved.